In an ongoing projective randomized controlled clinical trial (RFA award), we are comparing the treatment results of two commonly used therapies with differing modes of action on Class II, Division 1 malocclusion: head gear, and the Frankel functional appliance. There are few systematic, prospective longitudinal studies evaluating the effects of early (phase 1) treatment of this malocclusion, and controlling for the growth and maturational factors which may be associated with therapeutic outcome. The projected sample size was planned to include 80 white male and female patient selected in mid to late childhood, and randomly assigned to the two treatment groups which were stratified by severity of malocclusion and skeletal maturity. Our selection criteria were very stringent. Data collected consist of a series of measures made at different time periods. Evaluation of cephalometric data involves comparison of linear and angular measurements, as well as an improved method for detecting growth from superimposition on cranial, maxillary and mandibular bases. Dental casts taken bimonthly are measured for changes during treatment . Detailed growth, maturational and hormonal data are collected to determine the growth correlates of therapeutic outcome during the treatment period: monthly anthropometric measurements, including a new precise measure of knee height; monthly measurement of the salivary and quarterly measurement of the serum concentration of the adrenal androgen, dehydroepiandrosterone sulfate (DHEAS), which has been associated with the midgrowth spurt of childhood. Our working hypothesis relates to therapeutic outcome of the Frankel appliance on mandibular growth versus the headgear (which directly operates on the maxilla), controlling for skeletal maturity and severity of malocclusion. Other hypotheses involving the effects of variation of growth, maturation and hormonal change during the treatment period, are evaluated in order to determine more completely the correlates of the efficacy of early treatment. Our present population (60 enrolled, 50 remaining) includes mostly children in mid-childhood (45 enrolled, 38 remaining). In this competing renewal, we aim to recruit additional patients in late childhood, closer to the adolescent growth curve, to establish whether the effect of treatment by both or either appliance(s) is more significant in this age period. Successful treatment in late childhood may be timely enough to correct the malocclusion without the need to intervene in mid-childhood. Also, treatment in late childhood may require a shorter or no retention interval before a final therapeutic phase (phase 2) in which orthodontic appliances are used in the permanent dentition. A sample of 60 children, as determined by power analysis, projects the need for an additional 18 - 20 patients in late childhood. Significant results found to date underline the importance of this study and its continuation, which will provide a population for a future follow-up study of phase 2 that would include an appropriate control group of patients who have not received early treatment.